A display apparatus comprising a liquid crystal panel as an image display unit is configured to include a backlight device (light source device) at the back side of the liquid crystal panel, and to modulate the light emitted from the light source device at the liquid crystal panel which passes the light therethrough, to display an image on the front face of the liquid crystal panel.
Backlight devices are roughly divided into a direct type and an edge light type, of which back light devices of the edge light type have been widely employed recently in terms of lower power consumption and thinning of the devices.
A backlight device of the edge light type includes a light guide plate and a light source housed inside a backlight chassis having the shape of a shallow box with one face being open.
The light guide plate is a translucent plate made of resin, which is placed on the bottom plate of the backlight chassis.
The light source is fixed to the inner wall of the backlight chassis, and is opposed to one end face of the light guide plate.
A peripheral part of the light guide plate as well as the arrangement position of the light source are covered over an appropriate width by a frame fitted onto the edge of the backlight chassis through the open side.
The light emitted from the light source enters the light guide plate, then progresses while spreading inside the light guide plate, and is distributed across the entire surface of the light guide plate which is exposed to the inner side of the frame, to be output therefrom.
In order to increase the luminance of the light emitted from the light guide plate in this type of backlight device, it is important to assemble the device while maintaining the distance between the light guide plate and the light source that face each other as small as possible so that the light emitted from the light source may effectively enter the opposing end face of the light guide plate.
Meanwhile, the light guide plate may possibly be expanded by the heat generated at the light source, which causes a problem of damaging the light source by the expanded light guide plate touching the light source if the distance between the light source and the light guide plate facing each other is small.
The backlight device disclosed in WO2012/111549 is configured to have a restriction member arranged between a rectangular light guide plate and a light source opposed to one long side of the light guide plate, while a protrusion formed at both short sides of the light guide plate are engaged with a recess formed at the corresponding portions of the backlight chassis, and a leaf spring for applying a bias force toward the light source is interposed at the engaged part.
In the backlight device according to WO2012/111549, the light guide plate is positioned while being pressed against the restriction member by the bias force of the leaf spring, so that the distance between the light source and the light guide plate is maintained to be constant by the restriction member and the thermal expansion of the light guide plate is allowed because of the deflection of the leaf spring, which can increase the luminance and prevent damage to the light source.
The backlight device described in WO2012/111549, however, uses the leaf spring for positioning the light guide plate, which has a problem of the increased number of parts and a cumbersome work of interposing the leaf spring at the position where a recess and a protrusion are engaged.
Moreover, the backlight device in WO2012/111549 requires a wide frame for covering the peripheral edge of the light guide plate because the side wall of the backlight chassis provided with the recess is thick. This has caused a problem of difficulties in responding to the demand for a slim border in a display apparatus.
The present invention has been made in view of the circumstances described above, and aims to provide a light source device and a display apparatus capable of reducing the number of parts and of emitting light with high luminance while responding to the demand for a slim border.